Fine pitch wire grid polarizer

ABSTRACT

A fine pitch wire grid polarizer can have a pitch of less than 80 nanometers and a protective layer on the wires, by anisotropically etching the wire grid polarizer to form two parallel, elongated rods substantially located at corners where the wires contacted the substrate. The rods can be polarizing elements. A wire grid polarizer can have a repeated pattern of groups of parallel elongated wires disposed over a substrate. Each group of elongated wires comprises at least three wires. At least one wire at an interior of each group can be taller by more than about 10 nm than outermost wires of each group. Wires of a wire grid polarizer can be a byproduct of an etch reaction. A multi-step wire grid polarizer can comprise a base with a plurality of parallel multi-step ribs disposed on the base and a coating disposed along vertical surfaces of the steps.

CLAIM OF PRIORITY

This claims priority to U.S. Provisional Patent Application Ser. Nos.61/384,796, filed on Sep. 21, 2010, and 61/384,802, filed on Sep. 21,2010, which are hereby incorporated herein by reference in theirentirety.

BACKGROUND

Nanometer-sized devices, such as wire grid polarizers, can be limited inperformance by the distance between adjacent features, or the pitch ofone feature to the next. For example, for effective polarization ofelectromagnetic radiation, the pitch in a wire grid polarizer should beless than half the wavelength of the electromagnetic radiation. Wiregrid polarizers, with pitch smaller than half the wavelength of visiblelight, have been demonstrated. See for example U.S. Pat. Nos. 6,208,463;6,122,103; and 6,243,199. For higher polarization contrast and to allowpolarization of smaller wavelengths, such as for polarization ofultra-violet light and x-rays, smaller pitches are needed. Variousmethods have been proposed to solve this problem. See for example U.S.Pat. No. 7,692,860 and U.S. Publication numbers 2009/0041971 and2009/0053655.

A desirable feature of wire grid polarizers is to polarize a broadspectrum of electromagnetic radiation with a single polarizer. Wire gridpolarizers are typically formed with wires that are the same height. Itwould be beneficial to form wire grid polarizers with variable wireheight in order to allow tuning of the wire grid polarizer for multiplewavelengths and to allow for a smoother Ts curve. Methods have beenproposed for wire grid polarizers with different height wires. See forexample U.S. Publication numbers 20080037101 and 20080038467.

Wire grid polarizers are typically formed with wires that are situatedalong a single plane. It would be beneficial to form wire gridpolarizers with wires situated at multiple planes. A wire grid polarizerwith wires that are situated along multiple planes may be tuned tomultiple wavelengths and may allow for a smoother Ts curve. See forexample U.S. Publication numbers 20080037101 and 20080038467.

Wire grid polarizers are typically formed with wires that are allcomprised of single materials. A wire grid polarizer with some wirescomprised one material and other wires comprised of a different materialwould be beneficial for tuning the wire grid polarizer to multiplewavelengths.

SUMMARY

It has also been recognized that it would be advantageous to develop ananometer-sized device, such as a wire grid polarizer, with very smallspacing between adjacent features, i.e. small pitch. It has beenrecognized that it would be advantageous to develop a nanometer-sizeddevice, such as a wire grid polarizer in which there is variable wireheight, with wires situated at multiple planes, and/or with a wire arrayin which wires may be comprised of a different material than an adjacentwire.

The inventions described herein may have multiple uses, but a primaryuse is as a wire grid polarizer. The terms “wire grid polarizer” or“polarizer” will primarily be used for simplicity, but the invention maybe used for other purposes.

In one embodiment, the present invention is directed to a wire gridpolarizer comprising an array of parallel, elongated wires disposed on asubstrate, the wires having a pitch of less than 80 nanometers. Thiswire grid polarizer, with this small pitch, can be made by variousmethods described herein.

In another embodiment, the present invention is directed a method ofmaking a wire grid polarizer with fine pitch by obtaining a wire gridpolarizer having an array of parallel, elongated wires disposed on asubstrate, the wires having a protective layer disposed at a surface ofthe wires, then anisotropically etching the wire grid polarizer to formtwo parallel, elongated rods substantially located at corners where thewires contacted the substrate. The rods can be polarizing elements. Notethat the term “rods” is used to distinguish from the original wires. Inanother embodiment, a segmented film can be deposited on the rods. Thesegmented film can be used for polarizing or absorbing incomingelectromagnetic radiation. This method allows formation of at least twopolarizing rods from each resist feature, thus allowing for formation ofsmaller pitch wire grid polarizer. This method has an advantage of usingeach original wire to form two polarizing rods. The pitch of theoriginal wires can be limited by patterning abilities, but two rods canbe made for each original wire. The process can be repeated again,making two rails for each original rod. The term “rail” is used todistinguish from original wires and rods.

In another embodiment, the present invention is directed to a polarizerwith a repeated pattern of groups of parallel elongated wires disposedover a substrate. Each group of elongated wires comprises at least threewires. At least one wire at an interior of each group is taller by morethan 3 nanometers (“nm”) than outermost wires of each group. A distancebetween the outermost wires in each group is less than about 1micrometer. This embodiment has an advantage of variable height wires,such that one wire is taller than another. The wires can also have veryfine pitch.

In another embodiment, the present invention is directed to a polarizerwith an array of groups of parallel elongated wires disposed over asubstrate and comprising a material that is a byproduct of an etchreaction. A distance between outermost wires in each group is less thanabout 1 micrometer. This embodiment has an advantage of wires made byetch reaction. The wires can also have very fine pitch.

In another embodiment, the present invention is also directed to amethod for making a polarizer. The method comprises a resist over abase, then patterning the resist and creating resist widths. Anisotropic etch of the base can then be performed, etching bothvertically into the base laterally outside the resist and horizontallyunder the resist leaving a stem under the resist. Etch redeposition isallowed on the vertical sidewall of the stem, thus creating etchredeposition wires. The base outside the resist can also be etchedvertically, leaving a bottom step in the base. Etch redeposition isallowed to form on the vertical sidewall of the bottom step of the base,thus creating additional etch redeposition wires. This embodiment has anadvantage of wires made by etch reaction. The wires can also have veryfine pitch.

In another embodiment, the present invention is directed to a multi-stepwire grid polarizer device comprising a base with a plurality ofparallel multi-step ribs disposed on the base. Each of the ribscomprises multiple adjacent steps. A coating is disposed along verticalsurfaces of the steps. The coating along the vertical surface of anystep can be separate from the coating along a vertical surface of anadjacent step. Each multi-step rib may be formed under a single resistfeature. This embodiment has advantages of wires that can have very finepitch and/or wires situated at multiple planes, thus allowing the wiregrid polarizer to be tuned to multiple wavelengths.

In another embodiment, the present invention is also directed to amethod for making the above described device, the method comprising (1)forming multi-step ribs, the ribs attached to a base; (2) coating thesurface of the base and steps; and (3) removing thinner portions of thecoating on horizontal surfaces while leaving a majority of the coatingon vertical surfaces. This embodiment has advantages the ability to makea wire grid polarizer with wires that can have very fine pitch and/orwires situated at multiple planes, thus allowing the wire grid polarizerto be tuned to multiple wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional side view of a wire grid polarizerin accordance with an embodiment of the present invention;

FIG. 2 is a schematic cross-sectional side view showing one step inmaking a wire grid polarizer, in accordance with an embodiment of thepresent invention;

FIG. 3 is a schematic cross-sectional side view showing one step inmaking a wire grid polarizer, in accordance with an embodiment of thepresent invention;

FIG. 4 is a schematic cross-sectional side view showing one step inmaking a wire grid polarizer, in accordance with an embodiment of thepresent invention;

FIG. 5 is a schematic cross-sectional side view of a wire gridpolarizer, in accordance with an embodiment of the present invention;

FIG. 6 is a schematic cross-sectional side view showing one step in themanufacture of a wire grid polarizer, in accordance with an embodimentof the present invention;

FIG. 7 is a schematic cross-sectional side view showing one step in themanufacture of a wire grid polarizer, in accordance with an embodimentof the present invention;

FIG. 8 is a schematic cross-sectional side view showing one step in themanufacture of a wire grid polarizer, in accordance with an embodimentof the present invention;

FIG. 9 is a schematic cross-sectional side view showing one step in themanufacture of a wire grid polarizer, in accordance with an embodimentof the present invention;

FIG. 10 is a schematic cross-sectional side view showing one step in themanufacture of a wire grid polarizer in accordance with an embodiment ofthe present invention;

FIG. 11 is a schematic cross-sectional side view of a wire gridpolarizer, in accordance with an embodiment of the present invention;

FIG. 12 is a schematic cross-sectional side view of a multi-step wiregrid polarizer in accordance with an embodiment of the presentinvention;

FIG. 13 is a schematic cross-sectional side view of a multi-step wiregrid polarizer, in accordance with an embodiment of the presentinvention;

FIG. 14 is a schematic cross-sectional side view of a multi-step wiregrid polarizer, in accordance with an embodiment of the presentinvention;

FIG. 15 is a schematic cross-sectional side view of a multi-step wiregrid polarizer, in accordance with an embodiment of the presentinvention;

FIG. 16 is a schematic cross-sectional side view of a multi-step wiregrid polarizer, in accordance with an embodiment of the presentinvention;

FIG. 17 is a schematic cross-sectional side view of a multi-step wiregrid polarizer, in accordance with an embodiment of the presentinvention;

FIG. 18 is a schematic cross-sectional side view showing one step in themanufacture of a multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 19 is a schematic cross-sectional side view showing one step in themanufacture of a multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 20 is a schematic cross-sectional side view showing one step in themanufacture of a multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 21 is a schematic cross-sectional side view showing one step in themanufacture of a multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 22 is a schematic cross-sectional side view showing one step in themanufacture of a multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 23 is a schematic cross-sectional side view showing one step in themanufacture of multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 24 is a schematic cross-sectional side view showing one step in themanufacture of multi-step wire grid polarizer, in accordance with anembodiment of the present invention;

FIG. 25 is a schematic cross-sectional side view showing one step in themanufacture of multi-step wire grid polarizer, in accordance with anembodiment of the present invention; and

FIG. 26 is a schematic cross-sectional side view showing one step in themanufacture of multi-step wire grid polarizer, in accordance with anembodiment of the present invention.

DEFINITIONS

-   -   As used in this description and in the appended claims, the word        “electromagnetic radiation” includes infrared, visible,        ultraviolet, and x-ray regions of the electromagnetic spectrum.    -   As used herein, the terms wire, rod, rail, and rib are used to        describe various elongated structures having lengths        significantly longer than width or height. Wires, rods, rails,        and ribs can have various cross-sectional shapes. Wires, rods,        and rails can refer to polarizing structures in a wire grid        polarizer and ribs can refer to an elongated support structure        for wires.    -   As used herein, the term “substantially” refers to the complete        or nearly complete extent or degree of an action,        characteristic, property, state, structure, item, or result. For        example, an object that is “substantially” enclosed would mean        that the object is either completely enclosed or nearly        completely enclosed. The exact allowable degree of deviation        from absolute completeness may in some cases depend on the        specific context. However, generally speaking the nearness of        completion will be so as to have the same overall result as if        absolute and total completion were obtained. The use of        “substantially” is equally applicable when used in a negative        connotation to refer to the complete or near complete lack of an        action, characteristic, property, state, structure, item, or        result.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features illustrated herein, andadditional applications of the principles of the inventions asillustrated herein, which would occur to one skilled in the relevant artand having possession of this disclosure, are to be considered withinthe scope of the invention.

Fine Pitch Wire Grid Polarizer

As illustrated in FIG. 1, a polarizer 10 includes an array of parallel,elongated wires 12 disposed on a substrate 11. The substrate 11 can betransmissive of the wavelength of electromagnetic radiation used. Thewires can have a pitch of less than 80 nanometers. In one embodiment,the wires can have a pitch of 60-80 nanometers. In another embodiment,the wires can have a pitch of 8-85 nanometers. In another embodiment,the wires can have a pitch of 20-85 nanometers. In one embodiment, thewires can have a width w of less than 55 nanometers. In anotherembodiment, the wires can have a width w of less than 35 nanometers. Inanother embodiment, the wires can have a width w of less than 15nanometers. Polarizers, with pitch of 8-85 nanometers, may be used forpolarization of electromagnetic radiation having wavelengths of around16-170 nanometers. For polarization of such electromagnetic radiation,vanadium and hafnium can be good materials of choice for the wires 12.

The wires 12 can be formed of aluminum oxide; aluminum silicate;antimony trioxide; antimony sulphide; beryllium oxide; bismuth oxide;bismuth triflouride; boron nitride; boron oxide; cadmium sulfide;cadmium telluride; calcium fluoride; ceric oxide; chiolite; cryolite;cupric oxide; cupric chloride, cuprous chloride, cuprous sulfide;germanium; hafnium dioxide; lanthanum fluoride; lanthanum oxide; leadchloride; lead fluoride; lead telluride; lithium fluoride; magnesiumfluoride; magnesium oxide; neodymium fluoride; neodymium oxide; niobiumoxide; praseodymium oxide; scandium oxide; silicon; silicon oxide;disilicon trioxide; silicon carbide; silicon dioxide; sodium fluoride;silicon nitride; tantalum oxide; tantalum pentoxide; tellurium;titanium; titanium dioxide; titanium nitride, titanium carbide; thallouschloride; tungsten; yttrium oxide; zinc selenide; zinc sulfide;zirconium dioxide, and combinations thereof.

First Wire Grid Polarizer Manufacturing Method

FIGS. 1-4 show one method of manufacturing a fine pitch wire gridpolarizer. A wire grid polarizer 10, shown in FIG. 1, having an array ofparallel, elongated wires 12 disposed on a substrate 11, can have aprotective layer 21-22 disposed at a surface of the wires 12, as shownin FIG. 2. The protective layer 21-22 can be disposed at a top surface22 of the wires 12 and also at sides 21 of the wires 12. The protectivelayer 21-22 can be formed by passivation of the wires 12, and thus canbe embedded in the wires 12. The purpose of the protective layer 21-22is to make surfaces of the wires more etch resistant than centralportions of the wires.

The second step 30, shown in FIG. 3, is to anisotropically etch the wiregrid polarizer to form two parallel, elongated rods 32 substantiallylocated at corners 24 a-b where the wires contacted the substrate 11.The anisotropic etch can preferentially remove wires at a centralportion 25 of the wire 12, thus exposing the substrate 34 in thelocation of the former center 25 of the wire 12 while leaving wirematerial at corners 24 a-b. The central portion 25 is preferentiallyremoved because the protective layer 21-22 can be more resistant to theanisotropic etch than the wire 12 itself and thus after etching throughthe protective layer 22 on top of the wire, the anisotropic etchproceeds rapidly through the central portion 25 of the wire down to thesubstrate 34 while the side portions 26 of the wire etch more slowly dueto the etch resistant protective layer 21. Thus, the original wire isessentially cut in half, forming two rods 32 in place of the originalwire 12. Note, an alternative added step prior to the anisotropic etchis to ion mill the top of the wires 12, thus partially or totallyremoving the protective layer 22 prior to the anisotropic etch.

The two rods 32 can each be polarizing elements. Thus the wire gridpolarizer can now have twice as many polarizing elements as before thisstep 30. For example, in FIG. 3, rod group 32 a was formed of oneoriginal wire 12 a and rod group 32 b was formed of another originalwire 12 b. There can be a pitch P1 within a wire group and a pitch P2between groups. These two pitches can be the same or can be different,depending on the original wire width w, original wire pitch P, wirematerial, type of protective layer 21-22, and nature of etch.

Wire grid polarizers, without the fine pitch method 30 described above,have been made by standard lithography and etching methods with pitchesof around 100-150 nanometers and wire widths of around 50-75 nanometers.Thus, this method essentially cuts the pitch in half, allowing formationof wire grid polarizers by this method with pitches of around 50-75nanometers and wire widths of around 25-38 nanometers, even with presentlithography and etching methods.

An added step 40, shown in FIG. 4, that may be useful for some wire gridpolarizer applications is to apply a segmented coating 42 on top of therods 32. The segmented coating 42 can be aligned with the rods 32 andcan continue partially down both sides 43 of the rods 32 without coatingthe substrate 44 exposed between the rods 32. This segmented coating maybe applied by methods described in U.S. patent application Ser. No.12/507,570, filed on Jul. 22, 2009 and Ser. No. 13/075,470, filed onMar. 30, 2011, incorporated herein by reference.

Wire Grid Polarizer by Etch Redeposition

As illustrated in FIG. 5, a polarizer 50 includes a substrate 11 whichcan be transmissive of the wavelength of electromagnetic radiation used.For example, germanium could be used in the infrared, silicon in thevisible, and quartz in the ultraviolet. A repeated pattern of groups 53of parallel elongated wires 52 may be disposed on the substrate. Thewires 52 may comprise a material that can polarize the incidentelectromagnetic radiation. Each group 53 of elongated wires 52 cancomprise at least three wires. Each group can include one or moreinterior wires 52 c, such as one or more center wires, and outermostwires 52 o. The interior or center wires 52 c can be taller than theoutermost wires 52 o, such as by more than 3 nm in one aspect, more thanabout 10 nm in another aspect, more than about 20 nm in another aspect,or more than about 50 nm in another aspect. The distance between theoutermost wires 52 o, and thus the width d3 of each group 53, can beless than 1 micrometer in one aspect, less than about 150 nm in anotheraspect, less than about 100 nm in another aspect or less than about 50nm in another aspect. The wires 52 can be a byproduct of an etchreaction, which material can be beneficial for some applications. Thewidth d3 of each group 53 can be a resist width as will be describedbelow, thus multiple wires can be formed for a single resist width, thusallowing manufacture of a wire grid polarizer having very fine pitch.

Shown in FIG. 5 are two groups of wires 53 a and 53 b, each group havingfour wires. Two wires 52 c at the center of each group 53 can beapproximately equal in height and both can be taller than the outermostwires 52 o of each group, such that h1<h2. Center wires 52 c of a groupof wires 53 can be higher h2 than the height h1 of outer wires 52 o in agroup because center wires 52 c can be formed first during initialisotropic etch(es). Having wires of different heights h can allow tuningthe polarizer for different wavelengths and allow for smoothing out thes-polarization orientation of transmitted electromagnetic radiation overthe spectrum of incident of electromagnetic radiation, or the Ts curve.Having some of the wires higher can increase polarizer contrast whilehaving other wires shorter can improve transmission.

In one embodiment, center wires 52 c and outer wires 52 o can be madethe same height h, such that h2=h1, by methods such as chemicalmechanical polishing, fill and polish, spin on back etch, or other knownplanarization methods. Thus, a difference in height between the centerwires 52 c and the outer wires 52 o can be between about 0 nm to about150 nm, more than about 3 nm in one aspect, more than about 20 nm inanother aspect, or more than about 50 nm in another aspect, depending onthe strength, duration, and type of etch, the height of wires created,and whether the wires were planarized.

Shown in FIG. 5 is wire width w. Wire width may be determined by thetype of etch during creation of that wire 52, thin film material and/orsubstrate material, and whether adjacent wires combine to form a singlewire as described below in the description of FIG. 11. A maximum wirewidth of all wires 52 in the polarizer 10 can be less than about 150 nmin one aspect, less than about 50 nm in another aspect, less than about20 nm in another aspect, or less than about 10 nm in another aspect. Awire width w of one wire may differ from a wire width w of an adjacentwire by more than 5 nm in one aspect, more than 10 nm in another aspect,more than 20 nm in another aspect, or more than 50 nm in another aspect.

The distance between wires d in the groups of wires 53 can varydepending on the width of the resist and the nature and length of theetches. For example, a more lateral or stronger initial isotropic etchcan result in a smaller distance d2, shown in FIG. 5, between the centerwires 52 c in a group 53. A distance d1 between a center wire 52 c andan outer wire 52 o depends on the resist width R, as shown in FIG. 6,the distance d2 between the center wires 52 c, and the wire width w.Thus, by adjusting the parameters above, the distance d2 between thecenter wires 52 c can be different from the distance d1 between anoutermost wire and an adjacent center wire by more than about 3 nm inone aspect, more than about 10 nm in another aspect, or more than about20 nm in another aspect. In other words, the absolute value of d2 minusd1 can be more than about 3 nm in one aspect, more than about 10 nm inanother aspect, or more than about 20 nm in another aspect. A minimumdistance d between adjacent wires can be less than about 150 nm in oneaspect, less than about 50 nm in another aspect, or less than about 20nm in another aspect.

As shown in FIG. 5, pitch P is a distance between an edge of one wireand a corresponding edge of an adjacent wire. A minimum pitch ofadjacent wires can be less than about 300 nm in one aspect, less thanabout 100 nm in another aspect, less than about 50 nm in another aspect,less than about 30 nm in another aspect, or less than about 20 nm inanother aspect. The pitch of the wires can thus be much smaller than,even approximately one fourth the pitch of, the pitch of the resist.

A distance d4 between adjacent groups 53 can be determined a distance d5(see FIG. 6) between adjacent resist 61 and the width w of outermostwires 52 o in a group. This distance d4 may be modified for tuning ofthe polarizer for desired wavelengths.

As shown in FIG. 6, a polarizer of the present invention can be made bydisposing a resist 61 on a base 63. The base 63 can comprise a singlematerial or can be layers of multiple materials. For example, in oneembodiment the base 63 can comprise a thin film layer 62 disposed on asubstrate 11. The thin film 62 may be applied on the substrate 11 bymethods such as chemical vapor deposition or physical vapor deposition.The thin film may be a single layer of one material or may be multiplelayers of different materials. The substrate 11 can be a rigid materialsuch as quartz, silicon, or germanium. The substrate 11 can also be aflexible material such as a polymer.

The resist 61 may be patterned, providing resist widths R. The resistwidths R can be less than about 1 micrometer in one aspect, less thanabout 100 nanometers in another aspect, less than about 75 nanometers inanother aspect, or less than about 55 nanometers in another aspect. Theresist width R can be the approximate distance d3 between outermostwires 52 c in a group.

As shown in FIG. 7, an isotropic etch may then be performed, etchingboth vertically 71 into the base 63 laterally outside the resist andhorizontally 72 under the resist leaving a stem 73, having verticalsidewalls, under the resist 61. The aforementioned isotropic etch, or asubsequent isotropic etch can be optimized for etch redeposition by etchchemistry, thus allowing etch redeposition along vertical sidewalls ofthe stem 73 creating etch redeposition wires 74. The etch redepositionwires 74 can be polarizing wires and thus polarizing wires may be formedas a byproduct of an etch reaction.

As shown in FIG. 8, an anisotropic etch can then be performed, etchingvertically 71 into the base 63 outside the resist leaving a bottom step83, having vertical sidewalls, in the base 63. The aforementionedanisotropic etch, or a subsequent anisotropic etch can be optimized foretch redeposition, thus allowing etch redeposition to occur along thevertical sidewalls of the bottom step and creating additional etchredeposition wires 84.

Depending on the material of the base and/or thin film and the type ofetch, etch redeposition wires 74 & 84 can be comprised of a materialsuch as metal oxide, metal alloy, metal halide, metal carbide, andorganometal, or combinations thereof. Multiple isotropic etches beforean anisotropic etch, with each subsequent isotropic etch being lessisotropic in nature than the previous isotropic etch, can result in morethan four wires for every resist width R.

As shown in FIGS. 9-10, the anisotropic etch may continue, remove theresist, etch the base 63 between 91 the wires and substantially ortotally remove the base 63 between 101 etch redeposition wires 74 & 84,and leave at least four separate etch redeposition wires 74 and 84 forevery original resist width R.

As shown in FIG. 11, a group of wires can have three wires comprising acenter wire 112 c and outer wires 112 o. The method of making thisstructure is similar to that described above except that the stem 73 canbe smaller than if two center wires are desired. Thus, as etchredeposition starts on both sides of the stem 73, the stem 73 can besubstantially or completely etched away leaving a single center wire 112c rather than two center wires 52 c as shown in FIG. 5. The singlecenter wire 112 c can be higher than outer wires 112 o or can beapproximately the same height as outer wires as was described above forthe structure with at least four wires. If the center wires converge,and multiple isotropic etches are performed prior to the anisotropicetch, then there may be a structure with an odd number of at least fivewires in each group.

A structure with a single wire at the center of each group may bebeneficial if it is desired to have a large difference between widths ofwires in a group. As shown in FIG. 11, a width w1 of the center wire 72c, can be substantially wider than a width w2 of an outer wire 72 o of agroup.

Multi-Step Wire Grid Polarizer

As illustrated in FIG. 12, a multi-step, nanometer sized device orpolarizer 120 includes a base 121 with a plurality of parallelmulti-step ribs 122 disposed on the base 121. The term polarizer willhereafter be used, instead of nanometer sized device, because polarizeris the most typical application, but the device 120 can be used forother applications. Each rib 122 comprises multiple adjacent steps S ofdifferent heights h or disposed at different elevational heights. Eachrib 122 includes an upper step S1 with a top horizontal surface H1flanked by upper vertical surfaces V1. It will be appreciated that theterms horizontal and vertical are relative to the orientation of thedevice as shown in the figures, and that the device can be oriented atvarious different angles. Each rib also includes at least one lower stepor pair of steps (with one step on either side of the upper step) havingtwo horizontal surfaces, each flanked by a vertical surface for thatstep and by a vertical surface of an adjacent step. Thus, steps or pairsof steps are formed on both sides of the upper step, forming across-sectional stepped pyramid shape.

For example, the device in FIG. 12 shows two lower steps S2 and S3.Intermediate step S2 includes intermediate horizontal surfaces H2 andintermediate vertical surfaces V2. Intermediate horizontal surfaces H2flank the upper vertical surfaces V1 and intermediate vertical surfacesV2. Lower step S3 includes lower horizontal surfaces H3 and lowervertical surfaces V3. Lower horizontal surfaces H3 flank theintermediate vertical surfaces V2 and lower vertical surfaces V3.

The ribs can have more or less than two lower steps. Each step Sincludes a coating C along the vertical surfaces V of the step S. Thecoating C along the vertical surface V of any step S can be separatefrom the coating C along a vertical surface V of an adjacent (upper orlower) step S, such as by the intervening horizontal surface H. Thus, awidth or length HL of a horizontal surface H thereof can be greater thana thickness of the coating C. For example, in FIG. 12 there is nocontinuity of coating between the steps such that the coating C1 of theupper step S1 is physically separate from the coating C2 of theintermediate step S2 and the coating C2 of the intermediate step S2 isphysically separate from the coating C3 of the lower step S3. Thecoatings C can form pairs of coatings or coating pairs at differentelevational heights, such as an upper coating pair C1, and at least onelower coating pair, such as intermediate coating pair C2 and lowercoating pair C3. If the device is used as a polarizer, and a coating Cis selected that will polarize the wavelength of interest, then thecoating C may be considered to be a polarizing coating rib. Thus, thecoating may be a conductive coating and can define wires.

The upper and lower steps can be at different elevational heights hdefining a cross-sectional stepped pyramid shape. For example, in FIG.12, the elevational heights are not equal such that h1≠h2≠h3 andh1>h2>h3. The height of the steps can be determined by the depth ofetching. Some embodiments of the present invention can have anelevational height of the upper step that is less than about 200 nm inone aspect or less than about 100 nm in another aspect. The rib, orsteps or pairs of steps, can increase in width from the upper step sothat the rib has a cross-sectional stepped pyramid shape.

The coating material C can be or can include a metal such as aluminum,copper, germanium, titanium oxide, tantalum, or a metal alloy. Thecoating material C can also be a dielectric such as silicon, siliconcarbide, Fe₂Si, or hafnium. If the device is used as a wire gridpolarizer, the coating material C can be a material that optimallypolarizes the wavelengths of interest. For example, germanium could beused for infrared light, aluminum for visible light, or titanium oxidefor ultraviolet light.

As shown in FIG. 13, the base 121 of polarizer 120 b can comprise asubstrate 131 and at least one thin film layer 132. The substrate 131can comprise a material that is transparent to the incomingelectromagnetic radiation. The substrate 131 can be a rigid materialsuch as quartz, silicon, or germanium. The substrate 131 can also be aflexible material such as a casting film, polymer, or embossingsubstrate. The film layer 132 can be an anti-reflective coating, atransmissive film, an absorbing film, or other film with the desiredoptical properties.

The ribs 122 in the device can comprise the same material as the base121 and can be are integrally formed in the base 121, such as byetching, as shown in FIG. 12. Alternatively, the ribs can be physicallyseparate from the base, as shown in FIG. 13. In addition, the ribs 122can comprise a different material from the base 121. The ribs 122 cancomprise at least two layers of different materials. Each step cancomprise multiple layers of different materials. A step S can be made ofa different material than another step S. Each step S can be made ofdifferent materials. Multiple layers may be used for desiredpolarization characteristics, such as optimizing T_(p), T_(s), contrast,or absorption.

The coatings C can have very small widths CW. The width of the coatingcan be less than about 30 nm in one aspect, less than about 10 nm inanother aspect, or less than about 5 nm in another aspect. The coatingwidth can be selected or tuned based on the anticipated wavelength ofthe electromagnetic radiation and/or desired performancecharacteristics. Very narrow coating widths can be sustained by thestructural support of the rib or steps thereof.

As shown in FIG. 14, a rib 122 of a polarizer can have vertical heightsor length of vertical surfaces VL. In one embodiment, a vertical lengthVL of one step S can be the same as a vertical length VL of another stepS, or all other steps S. In another embodiment, a vertical length VL ofone step S can be different from a vertical length VL of another step S,or all other steps S. For example, the steps S can have substantiallyequal vertical lengths, VL1=VL2=VL3. Alternatively, the steps S can haveunequal vertical lengths, VL1≠VL2≠VL3. A polarizer with differentvertical lengths of vertical surfaces on different steps can havecoating of different heights. Each coating height can be tuned foroptimal polarization of a wavelength of interest. A difference ofvertical length VL of one step compared to any other step can be morethan 10 nanometers in one aspect, 10 to 50 nanometers in another aspect,50 to 100 nanometers in another aspect, or 100-200 nanometers in anotheraspect. For example VL1−VL2 and VL1−VL3 can be between 50 to 100nanometers.

The vertical lengths VL of steps S can be nanometer sized. For examplethe vertical length VL of any of the vertical surfaces can be less thanabout 100 nm in one aspect, less than about 50 nm in another aspect, orless than about 20 nm in another aspect. The vertical lengths VL can beselected or tuned based on the anticipated wavelength of theelectromagnetic radiation and/or desired performance characteristics.

The horizontal length of the widest step or outside width of thelowermost pair of steps, shown as SL1 in FIG. 14, can be approximatelythe width (see RW in FIG. 18) of the resist feature used to form thestep S. Resist features for presently manufactured wire grid polarizersfor visible light typically have a width of about 50-100 nm.Accordingly, the outside width SL1, and thus a distance between theoutermost coatings on a step, can be less than about 100 nm in oneaspect, less than about 75 nm in another aspect, less than about 50 nmin another aspect, or 50-100 nm in another aspect. Again, the width SL1of the outermost, lowermost pair of steps can be selected or tuned basedon the anticipated wavelength of the light and/or desired performancecharacteristics.

As shown in FIG. 15, a rib 122 can have a depth or horizontal length HLof the horizontal surface of a step that is the approximate pitchbetween adjacent coatings. The horizontal length HL of a step can beless than about 50 nm in one aspect, less than about 25 nm in anotheraspect, or less than about 10 nm in another aspect. A maximum distancebetween adjacent coatings can be less than about 50 nm and a minimumdistance between adjacent coatings can be less than about 20 nm. Thehorizontal length HL of all steps can be approximately the same.(HL1=HL2=HL3). The horizontal length HL of a step may be different fromthe horizontal length HL of other steps (HL1≠HL2 or HL1≠HL2 orHL1≠HL2≠HL3). The horizontal length of steps may be adjusted in order tooptimize polarization of the desired wavelengths.

The embodiments shown in FIGS. 12 & 13 have a step with the longest steplength SL as the lowest step or the step closest to the base. As shownin FIG. 16, a step, of a device 120 c or rib 122 c, with the longeststep length SL3 can be an intermediate step and a step with a shorterstep length SL5 can be the lowest step or the step closest to the base.

Also as shown in FIG. 16, the steps need not form a pyramid shape butrather the steps in the ribs can become wider or narrower moving fromthe outermost rib towards the base. The upper step can have the shorteststep length or another step can have the shortest step length dependingon the isotropic nature of each successive etch as described below. Thisembodiment may be useful for optimizing polarization of certain selectedwavelengths.

As shown in FIG. 17, wires 173 of polarizer 120 d may be disposed on thebase 121, physically separate from the multi-step ribs 122,substantially parallel with the multi-step ribs 122, and located betweenadjacent multi-step ribs 122. Coating C can be a dielectric or metal.Wires 173 can be dielectric or metal. Wires 173 can be a differentmaterial than coating C. This allows use of polarizing ribs made ofdifferent materials. This can be beneficial for tuning the polarizer tomultiple different wavelengths of electromagnetic radiation.

Multi-Step Wire Grid Polarizer—How to Make

A base 121 can be prepared with either a single material or with layersof different materials. For example, FIG. 13 shows a base 121 comprisedof a substrate 131 and a thin film 132. The ribs 122 can be the samematerial as the base 121, the same material as the substrate 131, thesame material as the thin film 132, or a different material than thebase, substrate, or thin film. As shown in FIGS. 14 and 15, the ribs 122can be made of layers. Each layer can be the same material as anotherlayer or can be a different material than another layer or layers. Eachstep S can be a different material than another step S. A single step Scan be made of multiple layers of different materials. Layers ofdifferent materials can be formed by applying thin films on a substratethrough processes such as chemical vapor deposition (CVD) or physicalvapor deposition (PVD).

The ribs 122 can be formed by depositing a material on a base 121 or byion milling into the base 121. The ribs 122 may also be formed in thebase 121 by etching the base as shown in FIGS. 18-21. For purposes ofthe description of FIGS. 18-21, the term “base” can include a singlematerial or layers of multiple materials. A resist 181 may be applied tothe base 121 and the resist 181 may be patterned to create resist widthsRW, as shown in FIG. 18. As shown in FIG. 19, an isotropic etch can etchboth vertically into the base laterally outside the resist 192 andhorizontally under the resist 191. At least one additional isotropicetch, that is more or less isotropic than the previous isotropic etch,may be performed. For example, as shown in FIG. 20, a second isotropicetch, which is less isotropic in nature than that shown in FIG. 19, isperformed to etch both vertically into the base laterally outside theresist 192 and horizontally under the resist 191. Each successive etchthat that is either more or less isotropic than the previous etch canresult in formation of an additional step. As shown in FIG. 21, ananisotropic etch may be used to etch into the base laterally outside theresist 192 and to remove the resist 181. The anisotropic etch can beused to create a step having a step length SL that is about the same asthe width of the resist RW.

Step horizontal length HL and step vertical length VL can be controlledduring step formation by the nature of the isotropic etches performed. Amore isotropic etch can create a longer horizontal length HL for a step.A longer etch time can create a longer vertical step length VL.

After the ribs have been created, the resist can be removed and thesurface of the structure may be coated with a coating C, as shown inFIG. 22. The coating may be conformal, non-conformal, segmented, atomiclayer deposition, spin on, or etch redeposition. The coating may then beanisotropically etched to substantially remove the coating fromhorizontal surfaces while leaving a majority of the coating on verticalsurfaces. The coating is removed from horizontal surfaces in theanisotropic etch, while leaving a substantial portion of the coating onthe vertical surfaces, because a thickness of the coating 222 on thehorizontal surfaces, in a direction perpendicular to the main plane ofthe base, as shown by dashed line P, is less than a thickness of thecoating 221 on the vertical surfaces, along this same direction P.

To form a structure as shown in FIG. 16, following the previouslydescribed anisotropic etch step to etch primarily in the area outsidethe width of the resist 192, additional isotropic etches 161 and 162 maybe performed. Various combinations of isotropic and anisotropic etchesmay be performed to create ribs of various shapes. After forming theribs, a coating is applied and etched as described above. Etching of thecoating can also remove coating along horizontal surfaces 163 that arebetween the multi-step rib 122 c and the base 121 by use of a high biasetch.

FIGS. 23-26 show how to make the polarizer 120 d of FIG. 17, whichincludes additional wires 173 in addition to coating C on multi-stepribs 122. As shown in FIG. 23, a thin first layer 171 can be disposed ona base 121. The material of this first layer 171 can be the desiredmaterial of the final wires 173, such as metal for example. A secondlayer can be applied over the first layer 171. The second layer can bethe desired material of the multi-stepped ribs 122, such as an oxide ordielectric for example. Multi-stepped rib structures 122 can then beformed as described above. The thickness of the second layer and theduration of the isotropic etch can be timed such that the etch stepsforming the multi-stepped ribs 122 end the surface of the first layer171. The final anisotropic step can be shortened in time in order toform a small final step. For example, a length of the vertical surfaceof the upper two steps VL1 and VL2 are significantly longer than alength of the vertical surface VL3 of the lowest step. As a result ofthe limited length of the vertical surface of the lowest step VL3, athickness of the coating in a direction perpendicular P to the base ismuch smaller along the vertical surface of the lowest step than alongthe vertical surface of upper steps.

A coating C can then be applied as described above. As shown in FIG. 24,the coating C thickness along a vertical surface of an upper step 241can be much longer than the coating thickness along a vertical surfaceof the lowest step 242. The coating thickness along the lowest step 242is not very much thicker than the thickness along a horizontal portionof the structure 243.

An anisotropic etch may be performed to remove coating from horizontalsurfaces and from the lowest step vertical surface 252. Due to therelatively smaller thickness of coating 242 along the vertical surfaceof the lowest step, as shown in FIG. 25, the coating can besubstantially removed from the vertical surface of this step 252 duringthis anisotropic etch of the coating while leaving the coating on thevertical surfaces of the upper steps 251.

An anisotropic etch, which is optimized for etch redeposition, may thenbe performed. The coating C, the second layer or rib 122 material, andthe etch must be selected such that primarily the first layer 171 willbe etched with minimal etching of the coating C or the ribs 122. Theetch can be optimized for etch redeposition by etch chemistry. Theanisotropic etch will etch into the first layer 171 and can result information of etch redeposition wires 173. The anisotropic etch cancontinue and thus remove the first layer 171 between 175 the etchredeposition wires 173 and the multi-step ribs 122, as shown in FIG. 17.The anisotropic etch may continue to etch into the base between the ribs174. The base 121 may thus be etched between 174 the wires 173 and themulti-step ribs 122 to a depth of at least 1 nm.

It is to be understood that the above-referenced arrangements are onlyillustrative of the application for the principles of the presentinvention. Numerous modifications and alternative arrangements can bedevised without departing from the spirit and scope of the presentinvention. While the present invention has been shown in the drawingsand fully described above with particularity and detail in connectionwith what is presently deemed to be the most practical and preferredembodiment(s) of the invention, it will be apparent to those of ordinaryskill in the art that numerous modifications can be made withoutdeparting from the principles and concepts of the invention as set forthherein.

1. A wire grid polarizer comprising: a. a substrate; b. an array ofparallel, elongated wires disposed on the substrate; and c. the wireshaving a pitch of less than 80 nanometers.
 2. The wire grid polarizer ofclaim 1, wherein the wires have a width less than 35 nanometers.
 3. Thewire grid polarizer of claim 1, wherein the wires have a pitch of 8 to85 nanometers.
 4. A method of making the wire grid polarizer of claim 1,the method comprising: a. obtaining a wire grid polarizer having anarray of parallel, elongated wires disposed on a substrate, the wireshaving a protective layer disposed at a surface of the wires; b.anisotropically etching the wire grid polarizer to form two parallel,elongated rods substantially located at corners where the wirescontacted the substrate.
 5. A polarizer, comprising: a. a substrate; b.a repeated pattern of groups of parallel elongated wires disposed overthe substrate; c. each group of elongated wires comprising at leastthree wires; d. at least one wire at an interior of each group is tallerby more than 10 nm than outermost wires of each group; and e. a distancebetween the outermost wires in each group is less than 1 micrometer. 6.The polarizer of claim 5, wherein the distance between the outermostwires in each group is less than 100 nanometers.
 7. The polarizer ofclaim 5, wherein a width of the wires is less than 20 nm.
 8. Thepolarizer of claim 5, wherein a minimum pitch of adjacent wires is lessthan 40 nm.
 9. The polarizer of claim 5, wherein the wires comprise amaterial that is a byproduct of an etch reaction.
 10. The polarizer ofclaim 5, wherein each group comprises at least four wires and a distancebetween two center wires is different than a distance between anoutermost wire and an adjacent center wire by more than about 3 nm. 11.A method for making the polarizer of claim 5, the method comprising: a.applying a resist over a base; b. patterning the resist and creatingresist widths; c. performing an isotropic etch of the base and etchingboth vertically into the base laterally outside the resist andhorizontally under the resist leaving a stem, having vertical sidewalls,under the resist; d. allowing etch redeposition along the verticalsidewalls of the stem creating etch redeposition wires; e. performing ananisotropic etch and etching vertically into the base outside the resistleaving a bottom step, having vertical sidewalls, in the base; f.allowing etch redeposition along the vertical sidewalls of the bottomstep and creating etch redeposition wires.
 12. The method of claim 11,further comprising etching to remove the resist, substantially removethe base between etch redeposition wires, and leaving at least threeseparate etch redeposition wires for every original resist width. 13.The method of claim 11, wherein the resist widths are less than about100 nm.
 14. A nanometer sized multi-step device, comprising: a. a base;b. a plurality of parallel multi-step ribs disposed on the base; c. eachrib comprising multiple adjacent steps on each side thereof, themultiple adjacent steps comprising: i. an upper step with a tophorizontal surface flanked by upper vertical surfaces; and ii. at leastone pair of lower steps having two horizontal surfaces on opposite sidesof the upper step, and flanked by lower vertical surfaces; d. a coatingalong the vertical surfaces of the upper step and the at least one pairof lower steps; and e. the coating along the vertical surface of anystep is separate from the coating along a vertical surface of anadjacent step.
 15. The device of claim 14, wherein the at least one pairof lower steps comprises at least two pairs of lower steps.
 16. Thedevice of claim 14, wherein the upper and lower steps are at differentelevational heights defining a cross-sectional stepped pyramid shape.17. The device of claim 14, further comprising wires which are: a.attached to the base; b. physically separate from the multi-step ribs;and c. substantially parallel with the multi-step ribs and locatedbetween adjacent multi-step ribs.
 18. The device of claim 14, whereinthe wires comprise etch redeposition material.
 19. A method for makingthe device of claim 14, the method comprising: a. forming multi-stepribs, the ribs attached to a base; b. coating the surface of the baseand steps; and c. removing coating on horizontal surfaces while leavingcoating on vertical surfaces.
 20. The method of claim 19, wherein themethod for forming multi-step ribs in a base comprises: a. applying aresist onto the base; b. patterning the resist to create resist widths;c. performing a first isotropic etch and etching both vertically intothe base laterally outside the resist and horizontally under the resist;d. performing at least one additional isotropic etch that is lessisotropic than the previous isotropic etch and etching both verticallyinto the base laterally outside the resist and horizontally under theresist; e. performing an anisotropic etch to etch into the baselaterally outside the resist and to remove the resist.